On Tue, Jul 28, 2009 at 7:59 AM, Seth Forshee <seth.fors...@gmail.com>wrote:

>
> On Tue, Jul 28, 2009 at 07:34:14AM -0700, San Mehat wrote:
> > I'll try your test code when I have a chance.
>
> Thanks.
>
> > > I'm in a difficult debugging sitation for this issue.  I can't build
> the
> > > kernel for the device (I'm working on getting the source to allow me to
> > > do this), and I don't have documentation for the processor.  I also
> > > don't know whether the msm_sdcc driver is using DMA or PIO for the
> > > transfer, although in my tracing of the code paths it doesn't look like
> > > it should matter because in either case the cache lines for the
> > > userspace mapping should be cleaned and invalidated before the transfer
> > > starts.  Are there any peculiarities of Android kernel modifications or
> > > of the MSM7k that could be causing this sort of behavior?
> > >
> >
>

Just an update on this, I've run your test program on a number of devices
with a few different brands of sdcards and haven't had a single failure.
Perhaps your unit is somehow faulty?

Thanks,

-san


> > I can't think of anything specific in the Android kernel patches which
> would
> > cause the behavior you're seeing.
> >
> > For SD cards basically we DMA for any transfers >= 64 bytes and which are
> 64
> > byte aligned.
>
> I'm having a hard time seeing where the problems would come from with
> DMA.  get_user_pages() should result in a clean/invalidate operation, so
> RAM should be consistent by the time the DMA operation starts.  If that
> were failing then all consumers of get_user_pages() would have a
> potential for problems.  Maybe I'm barking up the wrong tree with my
> cache aliasing suspicion, but then I don't know what else it could be.
>
> Thanks for the help.
>
> Seth
>
> >
>


-- 
----------
San Mehat
Staff Software Engineer
Google Inc.
o: 650-253-7422
c: 408-382-1249
s...@google.com

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